The flexural modulus of the neat PVC was
2.18 GPa with associated flexural strength of 49.0 MPa.
Both the flexural modulus and the flexural strength increased
as the rice hull content was raised from 20 phr to
60 phr as illustrated in Figs. 6 and 7. The composite with
maximal stiff at 60 phr rice hull content for all the particle
sizes was observed. This was expected because the
incorporation of the highly stiff and silica rich materials
likes rice hull to the PVC was the key parameter resisting
the flexure deformation. In contrast, there was a
downturn beyond 60 phr of rice hull for all particle sizes.
This was believed to be a result of the numerous agglomerations
of rice hull particles at high loading, as
shown in Fig. 9d. Several references also reported the
reduction of the flexural strength when particle agglomerations occurred in polyurethane/rice husk composites[
27,31], polypropylene/wood composites[8] and
expanded polystyrene/rice husk composites[26]. In
comparison, all of the PVC/rice hull compositions exhibited
higher flexural strengths than 44 MPa, which is
the flexural strength found in commercial WPCs. The
mechanical test results of the PVC/rice hull composites
evidently indicated that the waste rice hull without further
chemical treatments was an appropriate renewable
filler for the WPC production. Compared with natural
teak wood (Tectona grandis) and bamboo (Cephalostachyum
pergracile), the flexural strength of the teak
wood and bamboo are 144 MPa and 130 MPa, respectively,
corresponding to 140% and 116% higher than that
of the PVC/rice hull composites, implying that natural
solid teak and bamboo are much more rigid and stiffer
than the PVC filled with rice hull. For the industrial
application, the PVC filled with 60 phr rice hull is the
most appropriate compositions as natural wood replacement
due to their good mechanical performances
and suitability.